1. Field of Invention
This invention relates to a method of backside grinding a bumped wafer. More particularly, the present invention is related to a method of backside grinding a bumped wafer for protecting the devices and the bumps formed on the active surface of the wafer from being damaged at the duration of processing.
2. Related Art
In this information explosion age, integrated circuits products are used almost everywhere in our daily life. As fabricating technique continue to improve, electronic products having powerful functions, personalized performance and a higher degree of complexity are produced. Nowadays, most electronic products are relatively light and have a compact body. Hence, in semiconductor production, various types of high-density semiconductor packages have been developed. Flip chip is one of the most commonly used techniques for forming an integrated circuits package. Moreover, compared with a wire-bonding package or a tape automated bonding (TAB) package, a flip-chip package uses a shorter electrical path on average and has a better overall electrical performance. In a flip-chip package, the bonding pads on a chip and the contacts on a substrate are connected together through a plurality of bumps formed on the chip by a conventional bumping process and then an underfill material is filled into the gap between the chip and the substrate to encapsulate the bumps so as to well protect the bumps. In such a manner, the reliability of such flip chip package is enhanced.
As mentioned above, in order to have a thinner package, the step of backside grinding a wafer in a package process is necessary before the wafer is diced into a plurality of chips. Therein, before the wafer is diced, the active surface of the wafer is placed on a grinding film, and then the back surface of the wafer is thinned under a backside grinding process. However, usually, there are electronic devices formed on the active surface of the wafer, such as bumps, passive components, and metal posts, and are protruded from the active surface of the wafer without appropriate protection, so the electronic devices are easily fell away from the wafer at the duration of removing the grinding film from the wafer.
In order to well protect the electronic devices, there is a backside grinding method for a wafer level packaging disclosed in TW Pat. 516116, which utilizes an organic layer formed on a surface of a bumped wafer and a UV film (ultraviolet film) attached to the organic layer, regarded as a grinding film, to protect the bumps of the wafer at the processing steps. Therein, the organic layer is usually made of a material selected from Benzotriazoles and substituted Benzotriazoles as well known organic solderability preservatives (OSP). Usually, the organic layer is easily fell off from the wafer when the thickness of the organic layer is larger than 1 um. However, in order to well protect the bumps and similar electronic devices, the organic layer is usually required to have a thickness larger than 10 um. Therefore, the organic layer cannot be well adhered to the wafer to keep the bumps from being damaged. Besides, when the grinding film is removed, the organic layer is usually removed off with the grinding film so that the organic layer cannot be regarded as a protection layer when the wafer is diced.
As disclosed in US Publications 2002/0166625, there is disclosed another backside grinding method by using a grinding film with a base and a thicker adhesive layer provided therein. Therein, the thicker adhesive layer is made of a material, such as acrylic adhesive and ultraviolet film (UV film) so as to cover ten to sixty percents of bumps area. However, the interfaces between the bumps and the wafer are not well protected so that the interfaces are easily damaged. Besides, when the grinding film is removed from the wafer, the bumps are easily to be damaged so as to have some bumps fell off from the wafer.
Therefore, providing another method to solve the mentioned-above disadvantages is the most important task in this invention.